Plasma refers to the state of a gas ionized into negatively charged electrons and positively charged ions at an ultra-high temperature. In this state, the charge separation is very high, the numbers of negative and positive charges are equal, and thus the overall charge of the plasma is neutral.
Generally, the states of matter are divided into solid, liquid, and gas states. Since the state of plasma is different from the solid, liquid, and gas states, the plasma is often called the fourth state of matter.
When energy is applied to a solid, the solid becomes a liquid and then a gas, and when high energy applied again to the gas state, the gas is separated into electrons and atomic nuclei at a temperature of several tens of thousands of degrees Celsius.
In order to artificially create plasma, electrical methods such as direct current, ultra-high frequency, electric beam, etc. are required, and then this state should be maintained by a magnetic field.
To use the plasma in daily life, it should be artificially created in such a manner, but it can be said that the plasma is the most common state of matter in the universe. It has been assumed that 99% of matter in the universe is in the plasma state.
Lightning, aurora in the arctic, ionosphere in the atmosphere, etc. are in the plasma state. Outside the atmosphere, the plasma is also present in the Van Allen belt where the ions are trapped in the Earth's magnetic field and also in the solar wind coming from the sun. The interior of a star or the gas around the star is also in the plasma state. Hydrogen gas present in the space between stars is also in the plasma state.
Artificial plasmas that can be seen in everyday life include fluorescent lamps, mercury lamps, plasma display panels, etc.
Efforts to artificially create plasma and put it to practical use have been continuously made for a long time.
Plasmas are widely used, including plasma for nuclear fusion at a temperature of several hundreds of millions of degrees, low-temperature glow plasma or arc plasma used in semiconductor processes, synthesis of new materials, etc.
In particular, the low-temperature plasma is most widely studied and applied in industry. The reactivity is maximized in plasma, and thus the ionization and recombination of substances become active. Therefore, the use of plasma makes it possible to create a new substance, which is difficult to accomplish with the conventional synthesis or processing of substances, and replace the processes that cause pollution or that are difficult to perform.
Moreover, in a photolithography process, one of the manufacturing processes of flat panel display devices including liquid display devices or semiconductors, the plasma is used to remove a photoresist by ashing, which is used to pattern a metal material or semiconductor layer, to etch a thin film made of an organic material or semiconductor material, or to remove the organic material, etc. from the surface by cleaning.
As such, the plasma is widely used throughout the industry, and thus a variety of plasma generating devices for artificially generating plasma has also been commercialized.
Meanwhile, it has been reported that among the variety of plasma generating devices, some types of plasma generating devices that require carbon brushes have been applied.
In the case of this type of plasma generating device, a separate bearing is required to serve as a ground in the nature of its structure, and thus the damage to the ground bearing has been recognized as a major issue.
In practice, given that the main goal in the manufacturing process of flat panel display devices or semiconductors is to improve the productivity due to a reduction in tack time, if the maintenance of the plasma generating device occurs frequently due to damage to the ground bearing, etc., the operation of the device should be stopped during the maintenance of the plasma generating device, and thus the problem of damage to the ground bearing should not be easily overlooked. Therefore, there is a need to develop a new and advanced type of plasma generating device based on these matters.